The long term objective of this study has been to understand the mechanisms by which the collagenous matricies of bone and dentin become mineralized. These studies are of major importance for understanding in humans, bone and tooth growth and development, tissue remodeling, and mineralized tissue pathologies. These studies are also potentially important for the design of engineered biomimetic bone, tooth and cartilage replacement devices. They relate to the development of tissue strength and toughness, as well as their biochemistry and molecular biology. Our initial work showed that unique proteins were present in the extracellular matrix, and that their interaction with the collagen framework controlled placement, nucleation, orientation and growth of the mineral crystals. It is now recognized that there is a group of proteins (SIBLINGS) related by both sequence similarities and chromosomal location that carry out these functions in diverse tissues. Recent studies show that invertebrate mineralization systems share many similar mechanisms, suggesting that by comparing vertebrate and invertebrate mineralization processes a deeper understanding of relationships between matrix structure and the proteins directing mineralization may be developed. The present proposal focuses on two areas: the structure and composition of peritubular dentin (PTD) and its relationship to the intertubular dentin (ITD);and the identification and properties of the mineral- related proteins of the invertebrate echinoderm teeth. Specific aim 1 is to characterize the structure of the mineralized PTD, and to isolate and characterize its non-collagenous protein constituents.Unique secondary ion mass spectrometry (SIMS) will be coupled with classical biochemical approaches. The PTD plays a particularly important role in the structural properties of the coronal dentin in human teeth. Specific aim 2 is to identify the mineral-related proteins of the sea urchin, Lytechinus variegatus, teeth and examine their relationship to the vertebrate dentin proteins. Sea urchin teeth have remarkable mechanical properties in terms of strength and toughness, thus these studies are of particular interest in the design and creation of high strength biomimetic composite structures. They also reveal much about the evolution of vertebrate mineralized tissues. The skeletal tissues define our shape, provide structural stability, the means of loco- motion and our ability to do mechanical work. This study aims to understand how the skeleton is constructed.